Windmills have been used for many generations for the purpose of pumping water from the ground and for generating electricity. A basic advantage of the windmill is that it uses the power of atmospheric wind to rotate a wheel having radially extending blades. This rotary movement may be converted into various useful purposes. For example, wind turbines in the form of propellers mounted on towers have been placed in areas where steady winds are prevalent and the wind turbines are used to generate electricity.
The blades of the conventional wind turbines are very large and made of expensive rigid material and are constructed to have the blades extend radially from a central hub, with no extra support at the outer tips of the blades. The conventional wind turbine blades rotate at a high rate of revolutions and must withstand both the centrifugal forces generated by the fast revolution of the blades and the cantilever bending forces applied to the blades by the wind. Since the outer portions of the blades move at a very high velocity and are engaged by strong winds, the larger the blades the stronger they must be and the more expensive they become. Thus, there is a practical limit as to the length and width of the blades.
Another type of wind turbine is one that has sail wings constructed of fabric that are a substitute for the rigid blades of the conventional wind turbines described above. For example U.S. Pat. Nos. 4,330,714, 4,350,895, and 4,729,716 disclose wind turbines that use cloth “sails” that catch the wind. The blades of the wind turbine are formed of lighter weight material.
Another wind turbine type has rigid propellers that appear to be rigidly mounted to circular perimeter rims that support the outer ends of the propellers, as shown in U.S. Pat. Nos. 1,233,232 and 6,064,123.
Some of the wind turbines of the patents cited above are constructed with an outer rim that extends circumferentially about the turbine wheel. Rubber tires are placed in positions to engage the outer rim so as to rotate the rubber tires, with the driven rubber tires rotating the rotor of a generator. Thus, the rotation of the wind turbine is used to generate electricity.
Prior art wind turbines are mounted on upright towers and the towers are supported at their bases by mounting the towers in the earth or on some other stable platform. When the wind turbine is in operation with an oncoming brisk wind engaging the angled blades of the turbine wheel, a significant longitudinal force is transmitted from the blades of the turbine wheel to the upper portion of the tower, tending to tip the tower. This horizontal tipping force usually is significantly greater than the circumferential wind force engaging the angled surfaces of the blades of the turbine wheel and causing the rotation of the turbine wheel. This longitudinal force requires the tower for a wind turbine to be very strong to avoid tipping over.
While wind turbines have found use in open land areas where steady winds are prevalent, the land areas most suitable for catching the wind on wind turbine propeller blades usually are remote from the areas of great need of electrical power. Therefore, there is a requirement that electrical power be transmitted through conductive cables for long distances to the areas of need.
Winds generated over large bodies of water, particularly over an ocean, are not confronted with mountains, buildings, and the vegetation of the land masses that tend to slow the velocity of winds. The turbulence of wind usually is less over water than over land. This may be because there is a greater temperature variance between different altitudes over land than over a body of water, apparently because sunlight is absorbed further into water than into land, and for comparable conditions, the surfaces of land become warmer and radiate more heat than the surfaces of water.
Also, some of the largest cities of the world are positioned adjacent large bodies of water such as adjacent oceans and seas where wind velocities are not slowed and are less turbulent near the water surface and are more predictable.
Another advantage of wind turbines placed on bodies of water is that the less turbulent winds at the surface of the water allow the turbine wheel to be supported lower, closer to the surface of the water. This tends to reduce the expense of having a tall tower as usually required for land mounted wind turbines.
Accordingly, it would be desirable to locate wind turbines on bodies of water spaced relatively close to a land mass where there is a need for electricity. Also, it would be desirable to produce wind turbines with a means for reducing the longitudinal force applied by the turbine wheel to the tower or other vertical support of the wind turbine.